1. Field of the Invention
This invention relates to a recording apparatus and a recording method for attaining stable recording by use of head characteristics. More particularly this invention relates to a recording apparatus adapted to exalt image quality and ejection reliability by stabilizing the ejection behavior of a recording head and a recording method for use with the recording apparatus.
2. Related Background Art
Recording apparatuses such as printers, copying machines, or facsimiles are constructed so as to record an image of dot pattern on a recording material such as of paper or plastic film sheet in accordance with image data.
The recording apparatuses can be divided in terms of the manner of recording into the ink jet type, wire dot type, thermal type, laser beam type, etc. The recording apparatus of the ink jet type (ink jet recording apparatus), among other types mentioned above, is constructed to effect required recording by causing a recording head to eject ink (recording liquid) drops via nozzles thereof and allowing the ejected ink drops to land on and adhere to the recording material.
In recent years, a large number of recording apparatuses have been finding customers. These recording apparatuses are expected to satisfy the demand for high operational speed, high resolution, high image quality, or low noise. An example of the recording apparatus which answers the demand, the ink jet recording apparatus mentioned above may be adduced. One version of the ink jet recording apparatus attains recording by exerting thermal energy on the ink in the nozzles thereby inducing the ink to effervesce (or bubble) and utilizing the force of effervescence to eject the ink from the recording head. For the stabilization of the operation of ink ejection and the stabilization of the amount of ink to be ejected which are necessary for the accomplishment of the demand mentioned above, it is very important to control the temperature of the recording head and adjust the drive means used for the ink ejection.
For the conventional ink jet recording apparatus, therefore, it has been customary to adopt the so-called closed loop system which effects the detection of the head temperature by means of a temperature sensor incorporated in the recording head part or the method which, by means of a temperature calculating system capable of arithmetically estimating a change in the head temperature from the magnitude of the energy imparted to the head, detects the head temperature and controls the temperature of the recording head within a desired range on the basis of the detected recording head temperature or both of them.
As a means to allow compensation in the operation of the temperature detecting system mentioned above, JP-A-05-31,906 discloses a method which effects correction of the numerical data (stored as in a table) for use in the arithmetic operation on the basis of the difference to be found between the arithmetically estimated temperature and the temperature to be detected by the temperature sensor on the recording head while the recording head is in a thermally stable state. JP-A-05-31,918 teaches to effect the correction of the temperature of the temperature sensor on the recording head on the basis of the temperature which the environmental temperature sensing means built in the recording apparatus proper detects while the recording apparatus is not operating or not causing any change of temperature. Further, JP-A-05-64,890 teaches to use for the correction of the temperature of arithmetic estimation the difference between the arithmetically estimated temperature mentioned above and the temperature detected by the temperature sensor on the recording head. The methods of the inventions cited hereinabove by way of example aim to correct the head characteristics associated with such faulty factors attendant on the recording head of the exchangeable type as inconsistency among temperature sensors, error of heat time constant inherent in the recording head, and error of thermal efficiency of the recording head during the ink ejection, for example.
Generally, the aforementioned means for the arithmetic temperature estimation operate to estimate the temperature behavior (temperature increase) of a given object by measuring in advance the graduation of descent of the temperature of the object from the level to which the object has been heated by clocked supply of energy and calculating the sum of temperature required actually by the object in descending from the level elevated in the past per unit time to the existent level.
As a means to supply heat for the temperature control mentioned above, a heater member which is joined to the recording head is used. An ejection heater is used in the ink jet type recording apparatus which records an image with ink droplets ejected by means of thermal energy, specifically the apparatus adapted to obtain the ejection of ink droplets by means of growing bubbles by ink film boiling. When the ejection heater is adopted, it is kept energized to such an extent as to avoid spontaneously foaming.
The recording head which serves the purpose of generating ejection of ink particularly by virtue of the effervescence of the ink may be driven by a method of feeding electric current in the form of a single pulse or a double pulse or other similar multiple pulse to the ejection heater. Particularly in the drive using the double pulse waveform, the practice of controlling the waveform in accordance with the magnitude of the temperature of the recording head described above proves favorable because it permits easy control of the conditions of ejection such as the amount of ink to be ejected.
In order to set the drive conditions of the recording head, the drive conditions measured in advance are registered in the form of an incision on the head or storing them in a memory. An operator reads the data and sets the drive conditions.
To drive aptly the exchangeable recording head, recognition of the recording head operatively mounted in the recording apparatus is indispensable. For the sake of this recognition, a technique capable of causing the recording head to memorize identification data (ID) is available. This technique, however, demands time and labor for the work of memorization and, because of the necessity for providing each head with memory means (such as, for example, ROM), proves highly expensive. Then, for the purpose of enabling the ink jet recording apparatus to effect stable ejection of ink, the method for controlling the temperature of the recording head and the method for driving the recording head to eject ink constitute themselves important factors. Various methods have been developed and proposed. The method for driving the recording head in particular requires the driving conditions thereof to be optimized to counter various forms of inconstancy attendant on the head.
When the optimum driving conditions of the recording head are measured in advance and the data consequently obtained are stored in the memory, the operation of measurement and the work of incorporating the memory in the head result in exalting the overall cost of the head.
The fact that the aforementioned inconstancy found among individual heads depends particularly on the characteristics of the recording head has come to demand recognition. In the case of the ink jet recording head so adapted as to effect ejection of ink droplets by energizing the ejection heater and, by virtue of the heat consequently generated, inducing the ink to effervesce, for example, possible inconstancy of the magnitude of resistance of the ejection heater affects the energy to be imparted to the head and the manner of effervescence caused in the ink.
Further, the characteristics of the recording head which are manifested in the storage or release of heat possibly vary the characteristics of the effervescence and affect the driving conditions of the recording head, depending on the manner of conduction of the heat to be used for the effervescence of ink.
The recording head of the ink jet recording apparatus possibly fails to eject the ink normally as when it is left standing idly for a long time such that the ink gains in viscosity in the ink conduit particularly near the outlet of the nozzle. Besides, when the ink ejection is continued as when the recording is performed at a relatively high printing duty, the normal ink ejection is possibly obstructed eventually because minute bubbles occurring in the ink inside the ink conduit mentioned above grow in consequence of the continued ejection and the enlarged bubbles persist in the conduit and affect the ejection itself. These bubbles include those which enter the ink in the ink supply system, specifically through the joints used in the ink supply conduit, as well as those which are generated in consequence of the continued ejection mentioned above.
More often than not, the obstructed ink ejection mentioned above not only degrades the reliability of the recording apparatus but also damages the recording head itself and impairs the durability thereof possibly because the temperature of the recording head rises to an unduly high level from the normal one when the printing is continued at a high duty while the recording head remains in a state incapable of normal ink ejection.
To counter the obstructed ink ejection caused by the various factors mentioned above, the ink jet recording apparatus is subjected to various treatments for restoration of normal ink ejection such as, for example, a capping treatment which precludes the ink from gaining in viscosity by keeping the ink outlet mouth of the recording head covered while the ink ejection is not proceeding, an ink suction treatment which extracts the part of the ink of enhanced viscosity by aspirating the ink from the outlet mouth kept in the capped state, and a dry or idle ejection treatment which likewise eliminates the ink of enhanced viscosity by causing the ink to be discharged in much the same manner as during the normal recording onto a prescribed ink receptacle formed of an ink absorbent.
The treatment for restoration of the normal ink ejection has been automatically carried out at a prescribed interval as during the power connection to the apparatus or during the recording operation. Otherwise, it has been manually carried out by the user depressing a recovery button as occasion demands.
In the case of the ink jet recording apparatus adapted to undergo the treatment for restoration of the ink ejection during the power connection thereto, when the apparatus happens to be operated by a user who frequently turns on and off the power source, the number of occasions of his performing this treatment will excessively increase and the amount of the ink consumed and the amount of ink wastefully aspirated through the outlet will increase. In the case of the apparatus destined to undergo the manual treatment for restoration of the ink ejection performed by the user manipulating the restoration button at his own discretion, the treatment itself is at a disadvantage in lacking reliability because the user has no way of deciding whether the recording head is in the normal state or in the state incapable of ink ejection until he actually sets the recording head to action.
Regarding this problem, JP-A-04-255,361 which has issued to the present applicant for patent discloses a technique which is capable of deciding whether or not the recording head is ready to eject ink, depending on the rise of temperature caused in the recording head by dry ejection or the drop of temperature caused therein subsequently to the dry ejection. To be specific, when the recording head is in a state incapable of ejection, the rate of rise of the temperature or the rate of drop of the temperature is larger than when the recording head normally produces the ejection. When the rate of change of the rising and the dropping temperature (the sum of such rates, for example) exceeds a prescribed magnitude, therefore, it can be decided that the recording head has developed a state of allowing no normal ink ejection. (Hereinafter, this treatment will be referred to as an "ink failure detecting treatment.")
The rise of temperature which is caused in the recording head by dry ejection and utilized by the conventional technique for the detection of failure of ejection, however, is liable to fluctuate because of the characteristics of the recording head manifested in generation and storage of heat and the individual error of the recording apparatus proper manifested in voltage of the power supply. If the inconstancy in question is not inconspicuous, the detection of failure of the ink ejection cannot be obtained with high accuracy.